1. Field of the Invention
This invention relates to a negative-charging electrophotographic photosensitive member comprising an aluminum-based substrate and formed thereon a functional film having a sensitivity to electromagnetic waves such as light (which herein refers to light in a broad sense and indicates ultraviolet rays, visible rays, infrared rays, X-rays, xcex3-rays, etc.).
2. Related Background Art
In the field of image formation, photoconductive materials that form light-receiving layers of light-receiving members such as electrophotographic photosensitive members are required to have properties as follows: They are highly sensitive, have a high SN ratio [light current (Ip)/dark current (Id)], have absorption spectra suited to spectral characteristics of electromagnetic waves to be applied, have a high response to light, have the desired dark resistance and are harmless to human bodies when used. In particular, in the case of electrophotographic photosensitive members set in electrophotographic apparatus used as business machines in offices, the harmlessness in their use is important.
Photoconductive materials having good properties in these respects include amorphous silicon (hereinafter often xe2x80x9ca-Sixe2x80x9d), and have attracted notice as light-receiving layers of light-receiving members such as electrophotographic photosensitive members.
In the production of such light-receiving members, it is common to form photoconductive layers comprised of a-Si, by film forming processes such as vacuum deposition, sputtering, ion plating, heat-assisted CVD, light-assisted CVD and plasma-assisted CVD, which layers are formed on conductive supports while heating the supports at 50xc2x0 C. to 350xc2x0 C. In particular, their production by the plasma-assisted CVD is preferable and has been put into practical use; the plasma-assisted CVD being a process in which source gases are decomposed by high-frequency or microwave glow discharging to form amorphous silicon deposited films on the support.
For example, Japanese Patent Application Laid-open No. 57-115556 discloses a technique in which a surface barrier layer formed of a non-photoconductive amorphous material containing silicon atoms and carbon atoms is provided on a photoconductive layer formed of an amorphous material composed chiefly of silicon atoms, in order to achieve improvements in electrical, optical and photoconductive properties such as dark resistance, photosensitivity and response to light and service evironmental properties such as moisture resistance and also in stability with time, of a photoconductive member having a photoconductive layer constituted of an a-Si deposited film.
Japanese Patent Application Laid-open No. 6-83090 (corresponding to U.S. Pat. No. 5,464,721) also discloses a contact-charging, negative-charging electrophotographic photosensitive member provided on a photoconductive layer with a charge-trapping layer and a charge injection blocking layer which are formed of a doped a-Si, in order to perform sufficient charging even at the time of high humidity.
Japanese Patent Application Laid-open No. 6-242623 (corresponding to U.S. Pat. No. 5,556,729) still also discloses a technique in which a hole-capturing layer composed chiefly of amorphous silicon and also containing less than 50 ppm of boron or not containing any element which governs the conductivity is provided between a photoconductive layer and a surface layer, of a negative-charging electrophotographic photosensitive member to achieve superior electrophotographic performance.
Japanese Patent Application Laid-open No. 6-337532 (corresponding to U.S. Pat. No. 5,514,507) still also discloses a negative-charging electrophotographic photosensitive member having a photoconductive layer consisting of two layers, a layer composed chiefly of amorphous silicon and a layer composed chiefly of amorphous silicon germanium, in order to achieve a higher photosensitivity in a long-wavelength region and an improvement in stability in repeating copying operation.
In addition, Japanese Patent Application Laid-open No. 11-194515 (corresponding to U.S. Pat. No. 6,156,472) still also discloses a technique in which a silicate film is formed between a conductive substrate and a functional film to obtain an electrophotographic photosensitive member which can provide uniform and high-grade images.
The above techniques have brought about improvement in electrical, optical and photoconductive characteristics and service environmental properties, and, with such improvements, have brought about an improvement in image quality.
In recent years, with spread of computers and advance of networks in offices, electrophotographic apparatus are not only used as conventional analog copying machines but also now sought to be made digital so that they can play a role as facsimile machines or printers. Moreover, digital full-color copying machines for full-color reproducing digitized information are demanded.
If conventional positive-charging electrophotographic photosensitive members are mounted to digital full-color copying machines so as to meet such demands, the following problems are worried about.
First, as toners for color copying machines, used in the digital full-color copying machines, negatively chargeable toners are commonly used, where the formation of latent images which is performed in combination of such negatively chargeable toners with the positive-charging electrophotographic photosensitive members is made by a background exposure method in which non-image areas (background area) are exposed. Hence, this may make it difficult to achieve high image quality.
Second, in the digital full-color copying machines, it is chiefly intended to form images of full-page photographs, as being different from black and white copying machines which chiefly form images of letters or characters only. Hence, any minute unevenness in potential of photosensitive members may susceptibly affect the image quality, and this may make it difficult to control such unevenness.
For example, photo-memory as typified by ghost can be one of the causes of such unevenness. In conventional positive-charging electrophotographic photosensitive members, it is difficult in some cases to make the photo-memory less occur to a level required in full-color copying machines. Accordingly, it has been earnestly sought to provide an electrophotographic photosensitive member which can achieve ghostless images. However, in the conventional positive-charging electrophotographic photosensitive members, it requires a great effort to make the photo-memory much less occur. In conventional negative-charging electrophotographic photosensitive member, too, under the existing conditions, there is room for improvement on how the photo-memory can be made to much less occur.
Moreover, in the digital full-color copying machines, a plurality of developing assemblies are provided around an electrophotographic photosensitive member in some cases as one of process conditions, and, because of the use of a large-size developing means, a charging assembly and developing assemblies tend to be distant from one another in construction. This makes it necessary for the positive-charging electrophotographic photosensitive members of course and also the negative-charging electrophotographic photosensitive members to be electrostatically charged at a higher potential than ever to compensate the potential lowering at the distance from the charging assembly to the developing assemblies, and also, as to their photosensitivity, makes it necessary for them to have a higher sensitivity.
In order to materialize chargeability which is high enough to be adaptable to the digital full-color copying process, such chargeability can be materialized to a certain extent by forming the photoconductive layer in a large thickness. This, however, may make defects or imperfections occur in a high probability during the formation of deposited films to cause faulty images. There have been problems in respect of technique and also in respect of cost, bringing about a difficult situation.
The formation of latent images in digital copying machines is also the formation of latent images in the form of xe2x80x9cdotsxe2x80x9d. Hence, even smeared images at a level not coming into question in conventional analog copying machines may appear as coarse images in, e.g., halftone images. Thus, with regard to the smeared images, it is indispensable for them to be made to much less occur than those in the analog copying machines.
More specifically, in conventional photosensitive members, when the amount of exposure is enlarged so that an image with a strong contrast can be obtained from a color-background original, photo-carriers are produced in a large quantity because of application of intense exposure to cause a phenomenon that the photo-carriers gather to and flow into the part to which they can readily move. Because of this phenomenon, it is becoming more necessary than ever to take a countermeasure for smeared images in intense exposure, what is called smeared EV, which causes blurred letters or characters.
In addition, when the photosensitive member is negatively charged by the corona charging method, which prevails in charging methods in the conventional digital copying machines, ozone products are produced in a larger quantity than those in positive charging, and hence the smeared images may occur. Accordingly, the chargeability must be more improved than ever to keep ozone from being produced.
Taking account of the circumstances stated above, an object of the present invention is to provide, in a-Si photosensitive members, which have good stability and running performance, a negative-charging electrophotographic photosensitive member which can be improved in chargeability and sensitivity and can make photo-memory and smeared images less occur, both at high levels, and hence can dramatically be improved in image quality.
Stated specifically, according to an embodiment, the present invention is a negative-charging electrophotographic photosensitive member comprising an aluminum or aluminum alloy substrate and at least a film and a light-receiving layer which are superposed in this order from the substrate, wherein;
the film has a layer thickness of from 0.5 nm to 15 nm, comprises aluminum atoms, silicon atoms and oxygen atoms, and contains the silicon atoms in an amount of from 0.1 atomic part to 1 atomic part and the oxygen atoms in an amount of from 1 atomic part to 5 atomic parts both based on 1 atomic part of the aluminum atoms; and
the light-receiving layer has at least a lower-part charge injection blocking layer formed of a non-single crystal silicon film comprises at least silicon atoms, nitrogen atoms and oxygen atoms, not doped with any impurities; a photoconductive layer formed of a non-single crystal silicon film comprising at least silicon atoms; an upper-part charge injection blocking layer formed of a non-single crystal silicon film comprising at least silicon atoms, carbon atoms and atoms belonging to the Group 13 of the periodic table; and a surface protective layer formed of a non-single crystal silicon film comprising at least silicon atoms, carbon atoms, which layers are superposed in this order from the substrate.
According to another embodiment, the present invention is a negative-charging electrophotographic photosensitive member comprising an aluminum or aluminum alloy substrate and at least a film and a light-receiving layer which are superposed in this order from the substrate, wherein;
the film has a layer thickness of from 0.5 nm to 15 nm, comprises at least aluminum atoms, silicon atoms and oxygen atoms and contains the silicon atoms in an amount of from 0.1 atomic part to 1 atomic part and the oxygen atoms in an amount of from 1 atomic part to 5 atomic parts both based on 1 atomic part of the aluminum atoms; and
the light-receiving layer has at least a lower-part charge injection blocking layer and a photoconductive layer having a first photoconductive layer and a second photoconductive layer which are superposed in this order from the substrate;
the lower-part charge injection blocking layer being formed of a non-single crystal silicon film comprising at least silicon atoms, nitrogen atoms, oxygen atoms, and one of hydrogen atoms and halogen atoms, not doped with any impurities;
the photoconductive layer being formed of a non-single crystal silicon film comprising at least silicon atoms and one of hydrogen atoms and halogen atoms;
the first photoconductive layer containing atoms belonging to the Group 15 of the periodic table in an amount of from 0.01 atomic ppm to 10 atomic ppm based on the silicon atoms; and
the second photoconductive layer not containing any atoms belonging to the Group 13 of the periodic table.
According to still another embodiment, the present invention is a negative-charging electrophotographic photosensitive member comprising an aluminum or aluminum alloy substrate and at least a film and a light-receiving layer which are superposed in this order from the substrate, wherein;
the film has a layer thickness of from 0.5 nm to 15 nm, comprises at least aluminum atoms, silicon atoms and oxygen atoms, and contains the silicon atoms in an amount of from 0.1 atomic part to 1 atomic part and the oxygen atoms in an amount of from 1 atomic part to 5 atomic parts both based on 1 atomic part of the aluminum atoms; and
the light-receiving layer has at least a lower-part charge injection blocking layer and a photoconductive layer having a first photoconductive layer and a second photoconductive layer which are superposed in this order from the substrate;
the lower-part charge injection blocking layer being formed of a non-single crystal silicon film comprising at least silicon atoms, nitrogen atoms, oxygen atoms, and one of hydrogen atoms and halogen atoms, not doped with any impurities;
the photoconductive layer being formed of a non-single crystal silicon film comprising at least silicon atoms and one of hydrogen atoms and halogen atoms;
the first photoconductive layer containing atoms belonging to the Group 15 of the periodic table in an amount of from 0.01 atomic ppm to 10 atomic ppm based on the silicon atoms; and
the second photoconductive layer containing atoms belonging to the Group 13 of the periodic table in an amount of 15 atomic ppm or less.
The film may be formed using water containing an inhibitor. Where a silicate is used as the inhibitor, the film is referred to also as a silicate film. Also, the non-single crystal silicon is meant to include polycrystalline silicon and amorphous silicon (a-Si). It is common for the light-receiving layer of the electrophotographic photosensitive member to be produced from amorphous silicon.